The Great Pyramid of Giza is one of the Seven Wonders of the Ancient World, the oldest and the most intact of them all. Constructed in the third millennium BC, we marvel at all the labor and time it took to build it. We know it was constructed over a period between ten and twenty years, but the number of people who worked on it has been the subject of intense speculation for, well, forever. Since we don't know, maybe a better question would be how many workers would have been actually required to build such a massive pyramid.
We must start with the time constraint of roughly 20 years, the length of the reign of Khufu, the pharaoh who commissioned the construction (he died around 2530 B.C.E.). Herodotus, writing more than 21 centuries after the pyramid’s completion, was told that labor gangs totaling 100,000 men worked in three-month spells a year to finish the structure in 20 years. In 1974, Kurt Mendelssohn, a German-born British physicist, put the labor force at 70,000 seasonal workers and up to 10,000 permanent masons.
These are large overestimates; we can do better by appealing to simple physics. The potential energy of the pyramid—the energy needed to lift the mass above ground level—is simply the product of acceleration due to gravity, mass, and the center of mass, which in a pyramid is one-quarter of its height. The mass cannot be pinpointed because it depends on the specific densities of the Tura limestone and mortar that were used to build the structure; I am assuming a mean of 2.6 metric tons per cubic meter, hence a total mass of about 6.75 million metric tons. That means the pyramid’s potential energy is about 2.4 trillion joules.
Vaclav Smil crunches the numbers to come up with way fewer required laborers, in a very workable ratio of Egypt's population at the time. However, we all know that no work crew operates with 100% efficiency, because they are human. Read how the pyramids could have been built with smaller numbers than we assumed at IEEE Spectrum. -via Damn Interesting
(Image credit: L-BBE)